1. Field of the Invention
The present invention relates to the addition of microbeads to enhance the light emission, refraction or diffusion properties of heat-cured paint coatings. The invention relates to improved heat-curable paint compositions containing microbeads for producing painted surfaces, such as automobile bodies, having enhanced light-emission, light-refraction or light-diffusion properties, such as enhanced reflection, coloration, luminescence, phosphorescence and scattered light reflectability properties.
2. Description of Related Art
Microbeads and microspheres of glass, plastics and other materials, including those coated with conductive and reflective surface layers, are commercially-available for a variety of purposes, including use as light reflective fillers in paint and related coating compositions.
Reference is made to U.S. Pat. No. 5,650,213 for its disclosure of retroreflective coating compositions, such as for screen printing onto fabrics, containing hemispherically-metallized microsphere beads of 20 to 200 micron size, and transparent pigment particles of less than 2 micron size, having a color corresponding to the color of the substrate or desired image, to provide an attractive daytime image and daytime unnoticability. The coatings contain an aqueous matrix or binder material and have a final thickness of matrix which is less than one-half the diameter of the reflective beads.
It is known to add light-reflective glass beads, including hemispherically-metallized glass beads to opaque paint compositions such as for highway signs in order to provide dried paint surfaces, at or above which the beads are exposed. Light directed thereat, such as from automobile headlights, is retroreflected or reflected directly back at the source by the metallic bead coating or by brightly-colored pigments or an aluminum flake layer underlying the beads, which function as transverse lenses.
Reference is made to U.S. Pat. Nos. 2,879,171; 2,963,378; 2,997,403 and 3,251,704 for their disclosures of opaque, low solids paint compositions containing film-forming binder materials which dry by solvent evaporation, glass beads and opaque pigments. In U.S. Pat. No. 2,879,171 the coating particles exceed 50 to 2,500 micron size and the coating physically retains the 3 to 10 mil (75 to 250 microns) glass beads exposed at the outer surface of the dried paint to act as light reflectors. In U.S. Pat. No. 2,963,378 the low solids paint composition contains a major amount by weight of volatile organic solvents, 35 weight percent of reflectorized glass beads of 10 to 500 micron diameter and solvent-drying, film-forming binder materials to provide reflex-reflecting, non-diffusing coatings. The reflectorized glass beads may be mixtures of glasses having different refractive indexes, and their surfaces may be coated with transparent pigment or dye to retro-reflect in color. The coatings have glass bead protrusions and are covered with a top coating of transparent varnish, which may be colored, to provide a flat glossy surface.
U.S. Pat. No. 2,997,403 also discloses solvent lacquer spray compositions containing 25 to 40% by volume of glass beads of 0.0017 to 0.0024" (42.5 to 60.mu.) diameter for application over painted surfaces to provide retroreflective surface coatings.
U.S. Pat. No. 3,251,704 discloses low solids spray paint compositions containing hemispherically-metallized glass beads of different refractive indexes and sized between about 15 and 75 microns, and opaque pigment particles which do not interfere with the required reflex-reflection properties. The dried composition contains exposed glass beads as reflex-reflective lens elements.